|Vettel can win the World Championship in Singapore if he finishes 13 points clear of closest rival Alonso [GETTY]
Formula One championship leader Sebastian Vettel signalled he is on course to clinch the title this weekend by setting the fastest time in Friday's practice sessions for the Singapore Grand Prix.
However, the drivers were kept waiting when the opening practice was delayed by half an hour due to loose curbing. The session was subsequently reduced to only an hour rather than the scheduled 90 minutes.
The problem recurred late in the session when a bolt in the curbing came loose, prompting hasty repairs and a red flag. The curbing was removed at Turn 13 for the second session and was expected to be replaced before
Saturday's pre-qualifying practice.
Red Bull driver Vettel was two tenths of a second quicker than Ferrari's Fernando Alonso in the second session, with McLaren's Lewis Hamilton third fastest as the top three teams dominated.
Ferrari's Felipe Massa was fourth quickest around Marina Bay, with Red Bull's Mark Webber fifth and Mercedes' Michael Schumacher sixth.
Jenson Button's second session came to an end early after he failed to negotiate a turn and - unable to select reverse gear - was forced to leave his McLaren car parked on the circuit.
Vettel leads the championship by 112 points and if he gathers 13 points more than his closest rival Alonso on Sunday, then he would have successfully defended his title with five races to spare.
"I feel it's a weekend where we have a good car, looks like it's a competitive car to be able to fight for the podium," Vettel said.
"We still have to make adjustments overnight and do our homework."
While Vettel was not prepared to be too bullish looking ahead to Sunday, Hamilton acknowledged that Friday's performance shows the German will again be hard to beat.
| McLaren teammates Lewis Hamilton and Jenson Button face a tough challenge in Singapore [GETTY]
"We feel we were doing pretty well but then we were struggling with the rear tires," Hamilton said.
"They drop off very quickly and it's something we need to improve on.
"I suspect tomorrow there will be a gap in qualifying between us and (Vettel) unless there's a big difference in fuel load or something like that.
"Getting him will be very difficult but not impossible. The pace he had right now, it's very difficult for us to get to that kind of pace."
Toro Rosso driver Sebastien Buemi collided with one of the concrete barriers that hems in the tight street circuit, snapping the front right suspension.
Force India's Adrian Sutil was seventh fastest while his teammate Paul di Resta had little running due to a brake and hydraulic problem that had his car being rebuilt for much of the session.
The Sauber pair of Sergio Perez and Kamui Kobayashi were eighth and ninth on the timesheets, with Button in 10th.